Riku (Riku) is the head of the samurai of Nihonkoku.
Riku is a muscular, tanned skin man with black hair which is tied into a ponytail. When he was first introduced, he wore more traditional clothes consisting of a kimono top with the right half of his upper body uncovered and pants. After coming to World Line N, he wears more modern clothes such as a button up shirt and shorts.
As the head of the Nihonkoku samurai, Riku does his best to protect his people, making sure to take the underground passageways so that the Doume wouldn't know where they lived. He is friendly to outsiders, helping Sudou Kaname fight a Doume. He will obey orders, such as when he was ordered to arrest Kaname and his companions, nevertheless he will disobey orders if he decides to, as shown when he intended to throw the duel with Kaname which ultimately ended in a tie.
Skilled Fighter: As the head of the samurai of Nihonkoku, Riku is a skilled fighter.
Equipment: Riku is shown to use a spear when fighting the Doume with Kaname. He later receives the katana Doujigiri (童子切) from Minoru.